Core B. Clinical and Anatomical Pathology Core: Abstract The Clinical and Anatomic Pathology Core (CAP, Core B) will provide critical infrastructure support to the proposed `Revealing Reservoirs during Rebound' (R3) program. While antiretroviral treatment (ART) can effectively suppress HIV replication and prolong life of infected individuals, the virus persists in a latent state, only to re-emerge when ART is stopped. HIV-infected persons who interrupt their ART, offer a valuable opportunity to better understand how HIV persists throughout the body. The CAP Core is one of three Cores providing support services to R3 scientific Research Projects (RPs) to improve program efficiency. Overall, the CAP Core will oversee the collection, transportation, processing, and storage of biological samples from both existing cohorts and prospectively identified cohorts. Specifically, the Early Treatment RP will provide biological samples from existing and ongoing cohorts of HIV-infected individuals who initiated ART early after infection (Zurich Primary Infection Cohort and AIDS Clinical Trials Group A5345), had fully suppressed viremia for at least 48 weeks, and who later stopped therapy. The Late Treatment RP will evaluate biological samples collected from a prospectively recruited cohort of altruistic HIV-infected individuals on ART who have a terminal illness (e.g. solid organ cancer, cardiovascular disease) and who will voluntarily stop their ART before they die and then donate their bodies to the program (the `Last Gift' cohort). All of these samples will be used to measure cellular and tissue reservoirs of HIV to best understand how HIV reservoirs persist during ART and after voluntary ART interruption. Biological samples collected from the Early Treatment RP (blood plasma and PBMC) and Late Treatment RP (blood and full body tissues) participants will constitute the R3 Biorepository, managed by the CAP Core. The CAP Core will also support all clinical activities related to the Last Gift cohort including study enrollment, management, specimen collection, and post-mortem autopsy to address viral rebound patterns across a wide variety of tissue samples and will ensure that procedures related to biological specimen collection are safe and ethical. Overall, the CAP Core will address the following Specific Aims: 1) Support the Early Treatment RP with specimen shipping, storage and management; 2) Support Late Treatment Research RP with management of the Last Gift cohort; 3) Support Late Treatment RP with specimen shipping, storage and management from Last Gift cohort; and 4) Support the R3 Biorepository. The CAP Core will work collaboratively with the program RP and Cores to support coordinated development of the R3 Biorepository and appropriate access to research specimens. Together, these activities will provide efficiency throughout the R3 program.